Such a height adjustment, as shown, for example, by DE 35 02 579 A1, has a vertically adjustable strut that is formed from a shock absorber and a helical spring, and whose helical spring, which is clamped between two spring plates, can be adjusted by means of an adjustment device, which can be hydraulically activated in its free spring path proceeding from a normal level, by moving the upper spring plate that is attached to a cylindrical sleeve which lies coaxially to the shock absorber. The shock absorber is fixed with its piston on the body of the motor vehicle and on its outer cylindrical jacket bears the wheel-side, stationary spring plate.
Furthermore, DE 102 50 805 B4 shows an adjustable strut with its compression spring that acts in the impact direction and a hydraulic telescoping vibration damper that acts in the impact direction with a piston-cylinder assembly on which the compression spring is held by means of a spring receiver, and the length of the strut can be adjusted by moving the spring receiver on the piston-cylinder assembly in the impact direction. For this purpose, the piston-cylinder assembly has an outer thread and the spring receiver has an internal thread which engages herein so that the spring receiver can be moved by rotating the piston-cylinder assembly in its axial direction.
The known height adjustments which are variably adjustable between two end positions make possible a given defined deflection and rebound path for the existing helical spring out of the “normal level” position. The deflection path is limited by a stop buffer, the rebound path by the piston in the shock absorber. The size of these arrangements is limited by the narrow installation space in the motor vehicle. This causes conflicts of objectives for the design of this height adjustment, since the helical spring must not be too short; due to the danger of lifting of the helical spring of the spring plate in the rebounded state at the low level, a residual pretensioning force of approximately 500 N must, however, be present. The helical spring may also not exceed the allowable tensions at any operating point and may not be too long, that is, it can only have a limited number of turns, so that in the “high level” position and when completely deflected, the turns do not touch. Therefore, there must still be a relatively large turn clearance in exactly this position.
To be able to meet these requirements, according to the prior art the spring path of the helical spring is largely limited. For the critical case of “full deflection path at the high level” this compromise must be accepted since when the strut is set to the “high level,” the vehicle may travel off road. In this travel state it is of course not desirable for the full deflection path to be available. But the disadvantage is that in the “normal level” and “low level” positions the spring path is limited by the same amount as in the “high level” position, so that spring path is definitively lost.
Here the object of the invention is to eliminate these disadvantages.